13 replies to this topic

[lololol]

hello

how to choose a protection diode?

how to know which diode to choose

this is an example ; siemens siriuis contactor 24v DC  0.3A and the DIODE is 1N4007( 1A), many people use siemens contactors with diode 1N4007.

 

but if we have a contactor or solenoid  that consumes 12v 2A or 24v 4A how to calculate the diode?

thank you 

Edited by lololol, 08 December 2019 - 05:25 PM.

[MaMikee]

I think you mean 1N4007, that is a perfect snubbing diode choice.

 

7 cents each qty 100

[lololol]

yes of course sorry mistake 

 

 

but if we have a contactor 24v and 3A. or shaker 12v  3ampere.

we take diodes 4A example  : 

1N5401 - 100v - 3A -??

Edited by lololol, 08 December 2019 - 05:26 PM.

[mjr]

yes of course sorry mistake 

 

 

but if we have a contactor 24v and 3A. or shaker 12v  3ampere.

we take diodes 4A example  : 

1N5401 - 100v - 3A -??

 

Same answer - 1N4007. 

 

You might be getting a little confused about the purpose of the diodes here, when you bring "3A  contactor" or "3 ampere shaker" into it.  Here's what I'm picturing for your thinking process: "We have a 3A solenoid, so we need a diode that's rated for 3A.  But when I look at the 1N4007 data sheet, I see Io (average forward rectified forward current) is only 1A!  I need a bigger diode!"  Well, that would be true if you were installing the diode in series with the solenoid and asking it to carry the solenoid current all the time.  But you're not.  Remember that these flyback protection diodes get installed backwards.  They don't carry the forward current.  They only have to deal with the so-called "flyback" current that the solenoid generates when its power is cut.  The flyback current is a whole different thing with entirely different properties from the nominal Volts and Amps figures for the solenoid.  The 1N400x series turns out to be very well suited for the flyback protection job because it has a very high rating for reverse voltage (700V) and also a very high rating for peak forward current (30A).  By way of comparison, all of my real pinball machines from the 1980s and 1990s use 1N400x for this very job, so it's been the go-to diode that the pros have been choosing for this for a long time.

[lololol]

thank you for the answer.

I find strange that I always have the right and left diode are dead after a few weeks. the two contactors are 3 amperes.

But when I put siemens contactors 0.3A never problem, diode not dead.
Maybe

[mjr]

Well, the 1N4007 really should work for those, so I'm not sure why you're having them fail repeatedly.  Like I said, all of my 30-year-old pinball machines are equipped with 1N4003 flyback diodes for their 50VDC / 3-4A coils. 

 

Are you getting the diodes from a reliable source?  And you're using 1N4007, right?  Not one of the lower numbers in the same line, like 1N4001?  The higher the "x" in 1N400x, the higher the reverse voltage specs - you probably need to be using at least 1N4003 for any pin cab solenoid.

One other thing: in your original diagram, are you really connecting those 3A contactors directly to an LedWiz?  You know you can't do that, right? 

See "Power limits and boosters" here: http://mjrnet.org/pi....php?sid=ledwiz

I'm also curious what symptoms you're seeing when the diode fries.  Are you just getting out your diode tester regularly and testing it, or what?

[lololol]

Hello,

I always buy my diodes at conrad.com 1N4007 https://www.conrad.c...00-v-1-a-162272

I always connect my contactors with relay card, this photo is just found on google image.

 

 

when I play on the virtual pinball machine it happens that sometimes the power turns off, and there I know that it is the diode that is dead.

 

I take out the diode and I test it and there I find that it is conductive in both directions.

 

I put another diode and I keep playing for two months or sometimes two weeks. if the diode is dead and I insist on lighting the pinball machine, it bends two to three times and after that it is the contactors which no longer works.

 

thanks

[zebulon]

If the 4007 series are blowing consistently then you are exceeding 1A in the flyback voltage being generated.  Try going to 1N5408 ........ it's a 6A version of the 1N4007

 

Bear in mind that a diode isn't a brick wall stopping the voltage flow but more like a swimming pool with a small hole in it.  The voltage flows in faster than it flows out, reducing it to below the threshold that will trigger the load while it empties.  If that pool overflows (too much voltage) or the force of the flow (amperage) exceeds the capacity, the pool will rupture and stop functioning as it should (blown diode).

 

 

As you've found, when a diode fails it usually creates a dead short (continuity in both directions) by effectively becoming a piece of wire which is what is kicking out the power supply.  I would definitely put a fuse on the power supply line to the troublesome contactors as repeated failures are just beating up on the protection circuitry in your power supply and it will cause premature failure of the power supply over time.

Edited by zebulon, 14 December 2019 - 02:35 PM.

[mjr]

when I play on the virtual pinball machine it happens that sometimes the power turns off, and there I know that it is the diode that is dead.

I take out the diode and I test it and there I find that it is conductive in both directions.

 

Okay, that makes sense - that's consistent with having it installed correctly.

 

 

I always connect my contactors with relay card, this photo is just found on google image.

 

Good!  I was worried when I saw that diagram together with "4A contactor".  It's really the LedWiz that would have blown out in that scenario, not the diode, so it didn't seem like it could possibly be what was going on, but I figured I'd ask.

 

 

If the 4007 series are blowing consistently then you are exceeding 1A in the flyback voltage being generated.

 

Not just that, it means you're exceeding *30* Amps - the surge current rating for the 1N4007.  

 

Which is what makes me think you might have something else going on here that's going to make any diode you install blow, no matter how large it is.  (Like I said, the 1N4007 is used for even beefier coils in real pinball machines, so why is it blowing with these?)  That was why I asked how you know the diodes are dead: if the answer was "because the contactors stop working", I was going to guess that you had the diodes wired in series with the contactors so that they were carrying the fully 4A load every time the contactors turned on.  But it sounds like you have them wired right based on your symptoms, so maybe there's something else besides that something else.

 

One thing you could try is to insert a small resistor in series with the diode - maybe something on the order of 5 to 20 ohms (not "K" ohms, just plain ohms).  That would limit the flyback current going through the diode.  (But you want to keep that added resistance as small as possible, because the whole point is to provide a low-resistance local loop for the flyback.)

 

Coil(+)  ---- 5 ohm ---- |<Diode----- (-) Coil

Edited by mjr, 14 December 2019 - 07:12 PM.

[mjr]

I always buy my diodes at conrad.com 1N4007 https://www.conrad.c...00-v-1-a-162272

 

Well, here's something interesting: your vendor seems to be selling wimpier 1N4007's than other vendors.  Check out I[FRM] in the data sheet - they quote it at 10A, vs 30A for standard 1N4007.  (Or at least what I thought was "standard" - if you look at Mouser or Digikey, all of the 1N4007's they sell are rated at least 30A.)

On the other hand, their I[FSM] is 50A, and that's probably the stat that's applicable here.

[lololol]

thanks to both of you.

 

i will try both solutions, one with the small  resistor, and one with the 1N5408, i will test.

 

 

for information the right and left contacttors  solenoids are precisely the same solenoids that you have in your shop @zebulon.

 

it's cars switches just like the ones you sell, do you put 1N5408 diodes? with the complete system that you sell?

thank you guys 

[zebulon]

Nope, I use the sma (surface mount) equivalent of a 1n4007 without any issues.

[lololol]

like this https://picclick.fr/...3589324766.html

[zebulon]

Yes, those are what I put on my boards and they work fine.  They are a 1n4007 equivalent.